not long, if you cab is only 36 inches tall you take a couple inches away from the cfls then you take away the amount of space taken up by your pots or hydro system. I would guess your going to lose at least 6" in the pots and 8" for the cfls that leaves you about 22 inches for the plants. if you plan on using it just for veg I would guess you should be able to keep them in there for a month and a half to two months depending on the stretching ( I never grew with cfls only H.I.D. so i am not exactly sure how they with stretch for the light). If you want to flower in there you better get a lowryder type plant and run 12/12 from start.